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What is the function of the various inputs to a Lexium SD326 stepping motor drive?

The inputs of the SD326 are simple optocouplers which support either 5 volt logic signals or 24 volt logical signals depending on which interface cable is selected as an accessory.
(see attached image of typical optocoupler)

The reason optocouplers are used is because they support all types of output circuits found in typical PLC's
These optocoupler inputs support NPN, PNP and Push-Pull  (RS422) outputs. (see attached image of Signal Inputs of Stepper Drive)

Pulse input explained.
The pulse input is used to create step angular rotation of the motor. For each pulse that is applied to the pulse input the motor will make one step in rotational motion,
Therefore if we apply a square wave with a frequency of 1000hz the motor will therefore make 1000 steps per second.
The actual rotation speed is based on two elements.
1. The input frequency and
2. The step resolution which is selected via the step angle switches.

Example: If the step angle switches are set for 1000 steps per revolution. And we apply an input frequency of 1000hz, the motor will be making 1000 steps per second which is equal to the selected resolution so the motor shaft will be rotating at 1 revolution per second or 60rpm's

Example 2: If the step angle switches are set for 500 steps per revolution.
And we apply the same input frequency of 1000hz, the motor will be making 1000 steps per second which is equal to twice that of the selected resolution so the motor shaft will be rotating at 2 revolutions per second or 120rpm's.

The formula for calculating speed is RPM = a/360 * Fz * 60
Where as a = step angle and Fz = input frequency.

Step angle is calculated by 360 / the step resolution
Example 360 / 1000 = .36 degrees for each step in angular rotation

You will see in the manual for SD326 that the step resolution can be set at 200, 400, 500 and 1000 steps per rev. Also if micro step is activated these resolutions are 10x finer. ...2000, 4000, 5000 and 10000.

Simple divide 360 by the selected resolution to calculate step angle.
Example 2 360/500 = .72 degrees for each step in angular rotation.

Direction input explained.
The direction input is also an optocoupler. When this input is made true the motor will make step angular motion in a counter-clockwise direction when pulses are present at the pulse input.
When the direction input is not true normal rotational direction is Clockwise.

Gate/Enable input explained.
The Gate/Enable input servers one of two functions.
1. If the Gate/Enable switch on the front of the SD326 is in the ON position the signal input becomes a Gate input. The purpose of the gate input it to ignore pulses that are being applied to the pulse input when the Gate input is true. Therefore the Gate input will behave like a "Start/Stop" input

2. If the Gate/Enable switch on the front of the SD326 is in the OFF position the signal input becomes an Enable input. The Enable input is then used to turn the drive on or off.
The card is in an off state and if a signal is applied the the Enable input the drive will turn on.

PWM input explained.
The PWM input can be used to modulate the amount of current that is applied to the motor. This input is sometime known as a current null input.
The base current that is being applied to the motor is set via the rotary dial on the front of the SD326.
However, the output current can be modulated using the PWM input.
How this works is simple. The percentage of current reduction to the motor is based on the duty cycle of the signal applied to the zero current input.
Example.
If the motor current is set for 2 amps and a square wave signal is applied to the PWM input which has a duty cycle of 50 percent then the motor current is reduced by 50 percent which will be 1 amp.
The PWM input is used to reduce the motor current at stand-still so to control motor temperature from rising when motion is not needed.
In summary the PWM input can be used to reduce motor current while the motor is at rest. 
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